O,S-dialkyl phosphoramidothioates are effective insecticides. One particularly effective insecticide is O,S-dimethyl phosphoramidothioate (See, e.g., U.S. Pat. Nos. 3,309,266, 3,639,547 and 3,649,723, the disclosures of which are incorporated herein by reference). U.S. Pat. No. 3,309,266 discloses that O,S-dimethyl phosphoramidothioate can be made by reacting O,O-dimethyl chlorophosphorothioate with ammonia or a primary alkylamine and then heating the product of that reaction in the presence of an alkylating reagent such as an alkyl halide.
U.S. Pat. No. 3,639,547 discloses that O,S-dimethyl phosphoramidothioate can be made by reacting O,O-dimethyl phosphoramidothioate with the dimethyl ester of sulfuric acid or with a methyl ester of organic sulfonic acids. The reaction occurs at a temperature of from about 20.degree. C. to about 100.degree. C. In a manner similar to the method disclosed in U.S. Pat. No. 3,309,266, the O,O-dimethyl phosphoramidothioate can be made via ammoniation of a O,O-dimethyl halophosphorothioate.
With either of the above methods, the yield and purity of the formed O,S-dimethyl phosphoramidothioate are low, ranging from about 30 to 75 percent. There continues to be a need in the art, therefore for an efficient method for making O,S-dimethyl phosphoramidothioate.